The present invention relates to reactions of chlorosilanes and/or methoxysilanes with polysiloxanes which are particularly well suited for formulating intermediate silicone fluids and which may be used to methoxylate silicone rubber process aids.
Useful randomization reactions of chlorosilanes and/or methoxysilanes with chlorosiloxanes, methoxysiloxanes and siloxanes have been observed to occur without the addition of catalyst. Hydrochloric acid is present and presumably plays a significant role in the randomization reaction by breaking siloxane bonds and thus promoting rearrangements. It may be proper to refer to HCl as a catalyst since none of it is consumed during the overall reaction. However, it is of greater significance that no additional catalyst need be added to promote these reactions.
The use of acids to polymerize organosiloxanes and the scission and reformation of siloxane bonds is reviewed by W. Noll in the Chemistry and Technology of Silicones, Academic Press, 1966, pp. 219-226.
Of specific interest is the direct reaction of chlorosilanes and methoxysilanes with siloxanes. It is well-known that an equilibrium mixture of .alpha.,.omega.-dichloropolydimethylsiloxanes can be produced by the reaction Me.sub.2 SiCl.sub.2 (wherein Me represents methyl groups, --CH.sub.3) with octamethylcyclotetrasiloxane in the presence of FeCl.sub.3.6H.sub.2 O as follows: ##EQU1## The reaction will occur at room temperature or may be accelerated with mild heat such as by stirring at 50.degree. C. for 6 hours. This reaction is useful for preparing polysiloxane intermediates which can be incorporated into block copolymers or converted into rubber process aids.
Rearrangement and polymerization reactions of siloxanes in the presence of hydrogen chloride and aqueous hydrogen chloride as well as reactions between chlorosilanes and siloxanes can also be found in the art. Reactions between chlorosilanes and siloxanes which are used to prepare linear polychlorosiloxanes, are promoted by heat, pressure, presence of HCl, or the introduction of Lewis acid catalysts. Reactions of chlorosilanes and siloxanes as described in the patent literature may also be catalyzed by such compounds as phosphine oxides and amine N-oxides in polar solvents. From a practical point of view, addition of a catalyst has the significant advantage of rate acceleration under moderate process conditions but there remains a major disadvantage for many siloxane systems, namely, it is often very difficult to ultimately remove the catalyst or neutralize its effect. Residual catalyst can affect the ultimate properties of silicones. For example, the thermal life of some silicone resins may be reduced by the presence of residual iron salt catalyst exceeding about 5 to 10 ppm.
The customary process for preparing methoxy functional intermediate silicone fluids has involved adding MeOH--H.sub.2 O to a blend of chlorosilanes and then heating the mixture to reflux in order to drive the reaction toward completion, while removing dissolved HCl. The HCl content may be further reduced by washing with methanol; and finally the product is stripped in the presence of Celite and calcium carbonate by heating under reduced pressure. When this processing approach was used with a blend of 30 mole percent C.sub.6 H.sub.5 SiCl.sub.3 and 70 mole percent Me.sub.2 SiCl.sub.2, a reduction in yield of approximately 8 to 10 percent was obtained when compared to yields obtained with a blend having a composition of C.sub.6 H.sub.5 SiCl.sub.3, 331/3 mole percent; Me.sub.2 SiCl.sub.2, 331/3 mole percent; and (C.sub.6 H.sub.5).sub.2 SiCl.sub.2, 331/3 mole percent. The loss in yield may be attributable to stripping losses of volatile methoxydimethylsiloxanes formed in the process. The present invention provides a process which has an improved yield when compared to the above. The improvement is obtained through the interaction of combining the C.sub.6 H.sub.5 SiCl.sub.3 with the "hydrolyzate of Me.sub.2 SiCl.sub.2 " rather than with ordinary Me.sub.2 SiCl.sub.2.
Hydrolyzate of Me.sub.2 SiCl.sub.2 refers to the product of Me.sub.2 SiCl.sub.2 when it is hydrolyzed in a continuous loop fashion. The hydrolyzate contains approximately 60% (CH.sub.3).sub.2 SiO cyclic siloxane molecules of which [(CH.sub.3).sub.2 SiO].sub.4 and [(CH.sub.3).sub.2 SiO].sub.5 are the major components. The remaining 40% is composed of silanol chainstopped linear oligomers. The silanol level, however, generally does not exceed about 0.1 to 0.2% by weight. Use of the hydrolyzate of Me.sub.2 SiCl.sub.2 has some additional advantage in producing resins, since by-product hydrochloric acid from continuous loop hydrolysis of Me.sub.2 SiCl.sub.2 can be more readily recovered and recycled than the hydrochloric acid generated by Me.sub.2 SiCl.sub.2 in general resin processing.
Analogously, the "hydrolyzate of MeHSiCl.sub.2 " is a useful substitute for MeHSiCl.sub.2 in reactions for producing silicone polymers containing MeHSiO units.
It is therefore an object of the present invention to provide a novel process for the formulation of methoxy functional silicone intermediate fluids.
Another object is to provide a process for preparing methoxy chainstopped polydimethylsiloxane polymers.
Another object is to provide a process for preparing methoxy chainstopped polysiloxane polymers containing (C.sub.6 H.sub.5)SiO.sub.11/2 and MeHSiO units.
it is another object of the present invention to provide useful reactions of chlorosilanes and methoxysilanes with siloxanes without the addition of any catalyst nor with the need for carrying out these reactions in cumbersome pressure vessels.